1. Field of the Invention
The present invention pertains to self-propelled ground effect machines. More specifically, the present invention pertains to the mounting of motor-driven fans which provide air to support the machine and to propel it across land or water.
2. Description of the Prior Art
Ground effect machines, sometimes referred to a hovercraft, have existed for many years. These machines are vehicles for traveling across land or water which are supported above the surface of land or water on a cushion of air produced by one or more fans. Air from the fans is directed to a plenum chamber provided on the underneath side of the vehicle body. A flexible skirt of some type is provided around the plenum chamber to allow air to exhaust peripherally from the plenum chamber and skirt for support and to permit the vehicle to traverse on uneven terrain or choppy water. The fan supplies enough air to lift the vehicle on the cushion of air provided from the plenum chamber.
Air also supplies the power necessary for propulsion of the vehicle across land or water. The air for propelling the ground effect machine may be provided by the same fan which provides air to the plenum chamber or by another fan. In many cases, particularly with light ground effect machines, some type of air splitter or flow control device is provided which directs part of the air from a single fan to the air plenum chamber and part toward the rear of the vehicle for the propulsion thereof. Examples of ground effect machines may be seen in U.S. Pat. Nos. 3,687,217; 3,931,864; 4,666,012 and 4,828,058.
Fans, due to the angled disposition of the blades thereof, generate considerable twisting or spiralling of the air stream generated thereby. The percentage of kinetic energy expended on twisting or spiraling depends to a great extent on the number and spacing of fan blades and their pitch angle. The twisting or spiralling of the air stream from a fan has several undesirable consequences for small ground effect machines. The countertorque reaction of the fan acting along the elongated axis of the body thereof tends to induce roll along that axis. Energy is wasted due to the fact that air flow is not directed straight to the rear of the machine but at an angle from the longitudinal axis. Increasing air flow from a fan of a given diameter and rotational speed, requires more fan blades and more pitch and results in more twisting of the air stream, resulting in further inefficiencies and turbulence in the duct or shroud of the fan.
Various means have been used to try to straighten the flow of air from the fans of ground effect machines and to reduce the torque reaction and turbulence downstream thereof. Most of these efforts have been to provide some type of stator blades directly downstream of the fan blades to straighten the air and reduce torque reaction and turbulence thereof. While these methods are to various degrees effective, improvements are still needed.